<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    .cls {
      width: 300px;
      height: 200px;
      background-color: red;
    }
  </style>
  <script src="../../JavaScript/jQuery.js"></script>
  <script>
    $(function () {
      $('#btn1').click(function () {
        $('.cls').css('backgroundColor','yellow');
      });
    });
  </script>
</head>
<body>
  <button id="btn1">btn</button>
  <p class="cls">啊</p>
  <p class="cls">哦</p>
  <p class="cls">饿</p>
  <p class="cls">一</p>
  <p class="cls">五</p>
  <p class="cls">鱼</p>
</body>
</html>